package 过河卒;

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    static int N = 25;
    static long[][] f = new long[N][N];

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt() + 1;
        int m = in.nextInt() + 1;
        int x = in.nextInt() + 1;
        int y = in.nextInt() + 1;
        f[1][1] = 1;
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= m; j++) {
                if ((Math.abs(i - x) + Math.abs(j - y) == 3 && i != x && j != y) || (i == x && j == y)) {
                    continue;
                }
                if(i==1&&j==1){
                    continue;
                }
                f[i][j] = f[i - 1][j] + f[i][j - 1];
            }
        }
        System.out.println(f[n][m]);
    }
}
